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Zookeeper >> mail # user >> Network partition and ephemeral nodes


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Narayanan Arunachalam 2012-11-25, 18:32
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Camille Fournier 2012-11-25, 18:49
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Ted Dunning 2012-11-25, 19:40
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Re: Network partition and ephemeral nodes
In that case, a client using the lock recipe for instance, should keep an eye on disconnect event and abort the operation it started (the operation to be only run in the critical section), since there is no guarantee that it has the lock any more.

On Nov 25, 2012, at 11:40 AM, Ted Dunning <[EMAIL PROTECTED]> wrote:

> To expand on this, when a client is disconnected, it receives a disconnect
> event.
>
> From that time until the client is reconnected, the client doesn't know
> what has happened.  The session may have expired or it may have not
> expired.  Keep in mind that clock changes can make reasoning during this
> time impossible to do with precision.
>
> What the client does during this period of ignorance is up to the designer
> of the application.  There are several potential strategies.  If the
> application must have at most one master, then the disconnected client
> should immediately stop behaving as a master.  If the application must have
> at least one master, then the disconnected client should continue as
> master.  If you have an in between strategy where it is bad but not fatal
> to have two masters, you can have the disconnected client behave as a
> master up to the point where it thinks that it likely has been superseded
> by some other method.
>
> Zookeeper cannot decide this issue for you.
>
> On Sun, Nov 25, 2012 at 10:49 AM, Camille Fournier <[EMAIL PROTECTED]>wrote:
>
>> Yes if quorum is intact but the client cannot connect to the zookeeper, the
>> session and the ephemeral nodes will expire. It is up to users of ZK for
>> locking to correctly assume that a given client is not the lock holder if
>> its connection to the ZooKeeper is lost.
>>
>> C
>>
>> On Sun, Nov 25, 2012 at 1:32 PM, Narayanan Arunachalam <
>> [EMAIL PROTECTED]> wrote:
>>
>>> Hi,
>>>
>>> In case the network between ZK cluster and client is partitioned, once
>> the
>>> session expires would it remove the ephemeral nodes? If that's the case
>> how
>>> is the correctness of the recipes like locks are archived. Because once
>> the
>>> ephemeral nodes are removed next client would be granted the lock isn't
>> it.
>>>
>>> Regards,
>>> Nara
>>
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Ted Dunning 2012-11-25, 21:30
NEW: Monitor These Apps!
elasticsearch, apache solr, apache hbase, hadoop, redis, casssandra, amazon cloudwatch, mysql, memcached, apache kafka, apache zookeeper, apache storm, ubuntu, centOS, red hat, debian, puppet labs, java, senseiDB